1. Field of the Invention
The present invention relates to a liquid ejection head and a manufacturing method thereof, more particularly to a liquid ejection head comprising nozzles which eject liquid, and a manufacturing method thereof.
2. Description of the Related Art
A liquid ejection head has nozzles which eject droplets of ink toward a recording medium, such as paper. In the liquid ejection head, for example, it is known that by changing the volume of pressure chambers connected to the nozzles by means of actuators such as piezoelectric elements, through a diaphragm which constitutes one wall of the pressure chambers, the ink inside the pressure chambers is ejected from the nozzles.
The quality of the image formed on the recording medium by the liquid ejection head depends on variations in the ejection characteristics, such as the volume and ejection speed of the ink droplets ejected from the nozzles, and the like. The variations in the ejection characteristics are governed by variations in the dimensions of the sections relating to ejection, such as the nozzles.
On the other hand, a SOI (silicon on insulator) substrate having a structure in which a silicon layer is arranged on an insulating layer is known. There is a three-layer SOI substrate, in which a dielectric layer made of silica (SiO2) or the like serving as an insulator is formed on a supporting layer made of silicon (Si), and an active layer made of silicon (Si) is arranged on the dielectric layer.
Japanese Patent Application Publication Nos. 6-134994 and 9-216368 disclose technology where etching is performed from both surfaces of a SOI substrate (namely, the outer surface of the active layer and the outer surface of the supporting layer), thereby forming two holes whose bases reach to the dielectric layer, in such a manner that the centers of the holes coincide with each other, whereupon a nozzle hole passing through the SOI substrate in the thickness direction is formed by etching the dielectric layer from the side of one of the holes having the smaller base diameter.
Japanese Patent Application Publication Nos. 10-44406 and 2003-34035 disclose technology where pressure chambers are formed by etching the supporting layer of a SOI substrate, and the active layer and the dielectric layer of the SOI substrate are used as a diaphragm.
Dimensional variations in the nozzles which affect the ejection characteristics include, for instance, variation in the length of the nozzle and variation in the cross-sectional area of the nozzle. In general, the flow resistance of a circular flow path is inversely proportional to the fourth power of the diameter of the flow path, and the flow resistance of a square flow path is inversely proportional to the third power of the cross-sectional area of the flow path. Therefore, it can be seen that especially strict control of the cross-sectional area of the nozzles is required.
In Japanese Patent Application Publication Nos. 6-134994 and 9-216368, in practice, the nozzle length is defined on the basis of the thickness of the active layer of the SOI substrate and/or the dielectric layer, but on the other hand, the reduction achieved in the variation of the cross-sectional area of the nozzles is limited.
If, for example, nozzles having a diameter of approximately several micrometers (μm) to several tens micrometers are formed so as to pass through the substrate by photolithography and etching, then in practice, it is only possible to reduce the variation in the nozzle diameter to approximately ±0.1 μm to ±0.5 μm.
Japanese Patent Application Publication Nos. 10-44406 and 2003-34035 do not discuss reduction of the variation in the nozzle dimensions.